The present invention relates generally to automatic heating appliances, and more particularly to an appliance for automatically controlling heating to a cooking object on the basis of variation of the weight of the object to be heated.
Known are heating appliances with a plurality of different sensors which automatically controlling the time period of heating of an object in accordance with signals from the plurality of sensors such as humidity sensor, gas sensor and weight sensor. Using the plurality of sensors allows automatization of a wide range of cooking category. For example, the humidity sensor and gas sensor detect gases and vapors generated from the cooked object such as food and the results of the detection is used for controlling the termination of the heating of the cooked object. However, in the case of thawing of an object of a below-zero temperature, i.e., frozen food, the gases and vapors developed from the frozen foods are extremely few and generally the gas sensor and humidity sensor do not have sensitivities sufficient to detect them. Thus, a weight sensor is employed for the control of the termination of the heating, because the thawing time can be calculated by detection of the quantity of the frozen food. That is, the relative permittivity of ice is constant and the heating time period depends on only the quantity of the frozen food regardless of kinds of cooked objects. Accordingly, various sensors should be required for desirable automatization of cooking. However, provision of a plurality of sensors results in the appliance with a complex arrangement and a complex control system, thereby causing increase in the manufacturing cost.
On the other hand, various types of automatic heating appliances with only a weight sensor have been proposed heretofore. One known technique is that as disclosed in Japanese Patent Provisional Publication No. 62-66025 the termination of the heating is controlled by detecting the decrease in the weight of the heated food and then determining the kind of the food on the basis of the variation of the weight with respect to time during heating. There is a problem which arises with this type of appliance, however, in that the detection accuracy depends on the stability of the temperature characteristics of the weight sensor and the detection circuit therefor. One possible solution is to eliminate variation (drift) of the temperature characteristic of the weight-detecting devices, as disclosed in Japanese Patent Provisional Publication No. 62-168364, the technique of which involves detecting the atmosphere temperature of the weight-detecting devices and detecting weight of the food under the condition that the atmosphere temperatures at two timings are equal to each other so as to remove the detection error due to the variation of the temperature characteristic. However, this type of automatic heating appliance also provides problems that the use is limted to the oven cooking and a temperature detecting means should be required to detect the atmosphere temperature of the weight-detecting devices to result in a complex control system.